1. Field of the Invention
The present invention generally relates to a flat display panel assembly of a type operable with electron beams and, more particularly, to an electrode structure used in the flat display panel assembly.
2. Description of the Prior Art
An exemplary prior art flat display panel assembly is shown in FIG. 9 in sectional representation. The prior art flat display panel assembly shown therein comprises an evacuated glass envelope open at one end and having a generally flat faceplate 50 opposite to the open end. The faceplate 50 has an inner surface formed with a phosphor deposited screen 51 in the form of a plurality of parallel stripes of phosphor material. The open end of the glass envelope is closed by a backup glass plate 53. Within the glass envelope, there is disposed a rear electrode 54, and a plurality of parallel cathodes 55 each in the form of a wire and serving as a source of electron beams. Each of the cathodes 55 extends generally parallel to the rear electrode 54 and is held under tension by means of spring retainers 56 and has its opposite ends connected to the associated spring retainer 56 and the rear electrode 54. Reference numerals 57, 58, 59 and 60 represent respective electron beam controlling electrodes positioned on one side of the cathodes 55 remote from the rear electrode 54 in a substantially stacked fashion. Each of the beam controlling electrodes 57 to 60 has a plurality of electrode holes 57a, 58a, 59a or 60a defined therein in a predetermined pattern for the passage of electron beams therethrough towards the phosphor deposited screen 51. An assembly of the beam controlling electrodes 57 to 60 is secured to the rear electrode 54 by means of a plurality of bond deposits 61 of bonding agent. It is to be noted that the electrode holes in each of the beam controlling electrodes 57 to 60 are aligned with the stripes of the phosphor deposited screen 51. Thus, when the cathodes 55 are heated, electron beams B are emitted therefrom and are, after having passed through the electrode holes in the beam controlling electrodes 57 to 60, impinged upon the stripes R, G and B of the phosphor deposited screen 51 to excite phosphor dots on the phosphor deposited screen 51. The electron beams B scan, while being deflected, a region S1 delimited between solid and phantom lines thereby to form a color image.
The prior art flat display panel assembly of the construction described above has the following problem. Since the beam controlling electrodes 57 to 60 and the rear electrode 54 tend to undergo a thermal expansion under the influence of heat radiation from the cathodes during an operation of the flat display panel assembly, the electrode assembly as a whole increases in size. This will now be discussed in detail. FIGS. 10 and 11 show a right-hand portion of the flat display panel assembly of FIG. 9 on an enlarged scale in different conditions, respectively. Specifically, FIG. 10 shows a condition of landing of the electron beams before the electrode assembly undergoes the thermal expansion, whereas FIG. 11 shows a condition of the electron beam landing after the thermal expansion of the electrode assembly. As shown in FIG. 10, the electron beams having passed through the electrode holes 60a in one of the beam controlling electrodes which is closest to the phosphor deposited screen 51 scan, while being deflected, an end region S1. If the electrode assembly undergoes the thermal expansion under the influence of the heat radiation from the cathodes 55 as discussed above, the region at which the electron beams land varies as indicated by S2 in FIG. 11 and a mislanding occurs in which the electron beams no longer scan predetermined phosphor stripes at a periphery of the phosphor screen 51. Once this mislanding occurs, a color distortion occurs accompanied by a reduction in image quality.
FIGS. 12 and 13 illustrate different modes of thermal expansion occurring in the prior art flat display panel assembly. Specifically, FIG. 12 illustrates the mode of thermal expansion which occurs when a center pin 15-1 which is located in alignment with a geometric center of the electrode assembly is fixed. On the other hand, if a pin 15-2 which is located adjacent one end of the electrode assembly is fixed, the mode of thermal expansion occurring in the electrode assembly is such as shown in FIG. 13. FIGS. 12 and 13 make it clear that, in either case, the pins extending loosely through the electrode holes are laterally offset relative to those electrode holes.